1. Field of the Invention
The invention relates to the control of fuel mixtures for internal combustion engines to mitigate exhaust pollutants.
2. Description of the Prior Art
The use of oxygen sensors to control internal combustion engine fuel mixtures to exact stoichiometry is known. The control is necessary for catalysts, used to mitigate exhaust pollutants, to operate properly on the engines.
The control of a fuel mixture relies upon such oxygen sensors positioned before and/or after a catalyst used to mitigate the exhaust pollutants. The sensor or sensors provide signals to a fuel control system which varies the fuel mixture to achieve the best possible emission levels.
In a known single-sensor system, the sensor is placed before the catalyst (hereinafter termed “upstream” sensor) and its signal is fed back to a fuel control system which then varies the fuel mixture to achieve the best possible emission levels. Unfortunately, the sensors are subject to drift due to aging, environmental conditions, and engine operating parameters and conditions.
To correct for such problems, it is known to place a second oxygen sensor downstream of the catalyst (hereinafter termed “downstream” sensor). The downstream sensor is used to provide further control and correct any drift in the upstream sensor. However, the downstream sensor often sends momentary extreme signals to the upstream sensor, based upon a fuel anomaly in the content of exhaust gases. Such extreme signals cause a marked shift in the upstream controls which, in turn cause a further anomaly downstream
There is thus a need for a method for signal conditioning and reaction which may be used to perform controlling and corrective actions without momentarily extreme changes in operation of the catalyst.